


But It Can Glow, Too

by CryingKitten



Series: Blood Is Thicker Than Water [4]
Category: Undertale (Video Game)
Genre: About to Die, Above consent but just barely, Accidental Bonding, Accidental Soul Bonding, Aftermath of Torture, Aftermath of Violence, Alternate Universe - Underswap, Animalistic Sans, Bioluminescence, Biting, Blood Loss, Blood and Gore, Brother/Brother Incest, Brotp, Chara Is Dead, Chara Needs a Hug, Chara and Frisk Share a Body, Character Death, Denial, Depression, Established Alphys/Undyne, Extremely Dubious Consent, F/F, F/M, Forced Orgasm, Forced Pregnancy, Forced Sex, Forced Sex On A Lesbian, Forced Soulmates, Friends to Enemies, Future Character Death, Gore, Graphic Description of Corpses, Guro, Gurophilia, Human Looking Monsters, Human Papyrus, Human Sans, Human Souls, Humanoids, Icepick Lobotomy, Implied/Referenced Character Death, Insane Character(s)/Tropes, Just centered around Undyne, Kidnapping, Lobotomy, M/M, Masochism, Maybe - Freeform, Mentions of Necrophilia, Mentions of Pedophilia, Multi, Near Death Experiences, Non-Consensual Violence, Nonbinary Chara and Frisk, Old Medical Practices, Older Brother Papyrus, One-Sided Attraction, One-Sided Relationship, Other, Other Additional Tags to Be Added, POV Third Person, POV Undyne, Platonic Female/Male Relationships, Possessive Behavior, Possessive Sans, Post-Traumatic Stress Disorder - PTSD, Rape Aftermath, Rape Pregnancy, Rape Recovery, Rape/Non-con Elements, References to different fandoms, Sans Can RESET, Sans Has Seven Human SOULs, Sans Needs To Be Fucking Beat Up, Sans is a Creep, Self Humiliation, Self-Blame, Self-Doubt, Self-Esteem Issues, Self-Harm, Self-Hatred, Sexual Violence, Soul Bond, Soul Sex, Soul-Crushing, Soulmates, Stockholm Syndrome, Surgery On Self, Surviving Near Death, Undyne Is A Teen, Undyne Needs A Hug, Undyne likes cartoons instead of Anime in this, Unwanted Pregnancy, Vaginal Fingering, Vaginal Gore, Vaginal Sex, Victim Blaming, Violent Sex, Yandere Characters/Tropes, Yandere Sans, Younger Brother Sans, bioluminescent undyne, cheating death, monster souls, soulplay, victim shaming
Language: English
Status: In-Progress
Published: 2016-12-25
Updated: 2017-04-16
Packaged: 2018-09-11 22:17:08
Rating: Explicit
Warnings: Graphic Depictions Of Violence, Major Character Death, Rape/Non-Con, Underage
Chapters: 9
Words: 2,942
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9036605
Author URL: https://archiveofourown.org/users/CryingKitten/pseuds/CryingKitten
Summary: (Update as of 4/28/16: just a few edits, no real chapters.)You thought it was over?That's rich.Undyne was never confirmed dead, though it's a miracle she's alive. Here we see her story before the incident in which Sans 'snapped', during, and finally - after.





	1. Chapter 1

She idly cleaned at her desk, running a webbed hand over the wooden handle of her icepick.

 

From what she knew from the old, water-logged history books she found in the dump, this simple tool was some sort of life-changing experimental device that could cure all sorts of mental ailments.

 

She was planning on finding a test subject willing to participate, yet... 

 

The 'experiment' seemed rather cruel and evil. But it was in the name of science, right? So it'd be justified...

 

Right?

 

Either way, she was unsure on the idea of trying it, but wanted to give it a chance. Maybe the human she's been watching would want to help her, though that's doubtful.

 

Looking at her screen, she noticed that the human was talking with Papyrus, the six-year-old giving him "finger guns" and bursting into a fit of giggles after saying something to him.

 

She couldn't tell, considering her video feed was visuals only, so there was no audio, but she would bet it was something along the lines of something flirty. That's just what the humans seem to do.

 

She rolled her yellow eyes and returned to her work, washing off her tools for the umpteenth time today even though she never really uses them.

 

What she didn't see was the silhouette of Sans in the window of the brothers's house, chewing his glove with a look of pure and utter hatred before he quickly pulled the curtains shut.

 

What she didn't see was the killer grin her _oh-so-kind-and-innocent-and-caring_ friend had.

 

What she didn't see was the look sent directly to her hidden camera, a promise of something dark to come in the future.


	2. Chapter 2

"Listen, okay? Just fucking listen to me!"

 

"I-I am listening, but... that can't be true, Papyrus. I-I'm sorry!"

 

"Are you fucking serious, Undyne?! If you won't believe me, then I'll find somebody else. You're all fucking _crazy!"_ the humanoid stormed off before she could interject, and she whimpered.

 

She was never good with conflicts, and felt a tense feeling in her chest. Tears were already building up in her eyes, yet she quickly sighed shakily.

 

_I-it's okay. He doesn't mean it. And he was probably... just joking, right?_

 

_Yeah. Just joking..._

 

 

 

 

 

 

 _Either way, it's not like Sans would_ ever _act like that... right?_


	3. Chapter 3

**Summary for the Chapter:**

> "It's a brand new day, and the sun is high, all the birds are singing, that you're gonna die..."

When he opened the door, she smiled and looked up to greet him.

 

When she saw the blood, her smile dropped and she reached for a weapon at her desk. 

 

When he walked closer, her grip closed around the icepick.

 

She was never good with conflicts, but wouldn't want to sit by and let this happen.

 

She was a wimp, a coward, a _liar,_ but she wasn't going to go down easy. She's fought back the amalgamates every now and again, this would be just as easy, right?

 

When she held the weapon to him, he smiled and looked up to meet her eyes.

 

When she made a swing at him, he disappeared and formed behind her once again.

 

When she spun around to find him, he grabbed the wrist that had the pick and snapped it, forcing her to drop the weapon.

 

" _Cute._  You have so much _spunk,_ huh? I never expected you to fight me!" he giggled, like a child playing pretend, and tugged her closer by the wrist.

 

She had tears in her eyes, yet refused to make a noise for him. She won't fall, she won't quit. 

 

"Aww, what's _wrong?_ Now you're getting shy again?"

 

She didn't speak, just glared with so much hate and malice she could fuel the Underground for years on hatred alone.

 

"That expression... You won't give me the satisfaction, will you?" his grin grew, showing bloody, previously pure white and pearly teeth, teeth that grew in sharpness ever so slightly with each 'meal' of his so far.

 

"Don't worry, doctor, I'm _always_ up for a challenge." her eyes widened ever-so-slightly in fear. She didn't want to see what he'd do. 

 

"So why don't you be a good girl and... heh... stay 'tied up' for a bit?" as he spoke, burning ropes of magic constricted her wrists and ankles, making her fall to her back.

 

Her head smacked against the tiled ground, finned ears drooping and losing hearing while her eyes turned unfocused and blurry.

 

She heard somebody call her name, asking if she was okay, what was going on, what Sans was doing...

 

Then laughter, and a loud, _painful_ crash that made her ears ring, before she couldn't hold on any longer, and her eyes shut.

**Notes for the Chapter:**

> Kitten seems to like song-based chapters every now and again.


	4. Chapter 4

When she came to, she was in a world of mind-numbing pain.

 

The fin on the back of her head had been torn in the fall, most of the spines snapped or ripping through the thin skin between each of them.

 

Her head ached with each thrum of her SOUL.

 

Her wrists were raw from the rope.

 

Her glasses were askew and digging into her finned ears at a painful angle.

 

Once she gathered herself, she sat up, groaning with the effort. 

 

Around her was a... scene, to say bluntly, straight out of one of her _Courage the Cowardly Dog_ episodes.

 

The lab was a mess, ransacked, but a figure was lying near her feet. She scooted over, hands hovering over her mouth as she fought back the need to vomit. 

 

Even with her glasses dangling haphazardly off of her face, she'd be able to recognize them from anywhere.

 

Their body was in its NEO form.

 

The blue liquid of their SOUL that fueled their body like oil was dripping from their silvery hair, hat missing from their transformation and thrown across the room. Their gun was smashed, a visible footprint seen in the destroyed black metal, leaking the same fluid.

 

They weren't moving an inch, and she soon found out why.

 

Their SOUL was missing from its vulnerable space between their legs and torso, and there was a sharp point sticking out from the back of their head, soaked in blue yet the silver still gleamed in the light.

 

She scooted closer, holding her wrists to the point and trying to saw off the ropes.

 

_They wanted to save you._

 

_They wanted to save themself._

 

_They loved their body, they'd never blame you._

 

_You left them open for attack, it's all your fault._

 

_They cared about you like they cared about their cousin._

 

_And they left their cousin behind once they reached stardom._

 

She fought back sobs, breathing heavily when the ropes snapped from her wrists, and she quickly tried to untie her ankles. 

 

 _They didn't go down without a fight,_ she assured herself, _and they don't want you to, either._


	5. Chapter 5

She knew that he was strong. She didn't dare to test that theory.

 

She never opened the doors or anything, and was slowly running down her supply of popato chisps, brand-name colas, and microwaved macaroni. 

 

She never disrupted their body, but when she found their hat, she couldn't just leave it be.

 

She took the blue and white accessory in her webbed hands, worrying her bottom lip as she thought. 

 

She walked over to her desk, setting it down next to her currently headless Gir plushy, whose head was torn off by _you-know-who_ during _you-know-when._

 

She took a breath to calm herself, looking over to their body.

 

 _How long has it been, Undyne? How long have you sat here and rotted with me?_ their voice echoed in her head, and she tightly shut her eyes to shake off the guilt.

 

If she had just listened to Papyrus, they would be alive.

 

He would be safe...

 

 _She_ would be alive...

 

 _And it's all my fault, isn't it?_ the voice was hard to recognize as hers, even as she mouthed it while it was spoken in her head.

 

She had changed so much, her head-fin shredded with chipped and missing spines, her hair was a tangled mess...

 

She hadn't even noticed she was standing over them until her hand was running through their soft, silver hair.

 

She flinched when something pricked her, and she pulled back as if she had been burned to nothing but a crispy fish-stick.

 

Looking at the needle-like point, she frowned.

 

 _"I'm sorry."_ she mumbled to their lifeless corpse as she turned them over with a bit of effort, making them roll onto their back.

 

Dust was unsettled, and a single spider had skittered out from under them once it noticed her. At least the spiders were still here with her, huh? Still on her side?

 

Probably not. They'd hate her after what she's done. She'd hate her, too.

 

_I do._

 

She sighed -  _Focus, Undyne!_ - before she took an unwilling look at their face.

 

The icepick was jammed through their right eye, and she took the handle with shaking hands.

 

 _"I'm so sorry..."_ she mumbled, as if that would do anything by now, and began trying to pull it out. It stuck stubbornly, and she quickly had to tug it a few times before it finally gave.

 

She whimpered at the noise of wires being torn, as if she was the one who had to go through all of that - all of _this_ \- pain.

 

_Pitiful._

 

She bit her lip until it started to bleed, the cyan drawing attention to her red-painted lips. 

 

She didn't even notice. It tasted so... chemical. So _foreign, a_ nd yet... it felt so, _so_  good. So _right_. 

 

She was losing it.

 

She wouldn't let him have this, she decided, she wouldn't let him win.

 

_I'll fix this..._

 

_I have to._


	6. Chapter 6

She took a deep breath, looking at her hand.

 

She tightly held the grip of the icepick, as if it was the last thing connecting her to this world.

 

What she wouldn't give to have this all be some sort of morbid nightmare, a game at the hands of a cruel master who will hopefully get bored, an author who will run out of fans to keep the embers alight and the fire flickering...

 

She just wished this was all in her head.

 

_You should just hurry up and do it. Or are you too useless for that, too? It explains how you let my body get destroyed._

 

She wiped at tears that just began to fall, sniffling.

 

 _You don't deserve to cry. You got off easy,_ their voice chastised her, _and you didn't have to suffer through the pain like all of us. Just do it. Stop him. Useless._

 

"Alright... Sans... I-I'm not going to let you win. You're-you're... going down. It's what she would've wanted..." her voice cracked, but the sudden smug and confident figure now behind her just made the growing pit in her stomach ever worse.

 

"Oh? Am I now?" he purred, a gloved hand landing on her waist. She jumped, and he just giggled, the hand beginning to trail upwards and towards her chest. "You're _cute_ when you're trying to achieve the impossible, Doctor." he all but purred, tracing the skin that was left bare by the large holes sewn into her shirt to keep the gills on her chest from being restricted.

 

"L-let go of me!" she tried to shove away, yet he tightly pressed a foot to her ankle and she tripped, her weapon skidding away.

 

"Aww, and you were so sure of yourself earlier." he clicked his tongue as she desperately reached for the pick, only to be flipped onto her back. "Guess I'll have to show you what happens when you mess with a **g o d** ." his teeth grew sharper, left eye glowing a bright white in a vaguely heart-shaped pattern, before he grabbed the pick that was just barely out of her reach.

 

He held it to her palms with a proud and demonic grin, while they frowned at her from over his shoulder.

 

_Don't fight it. You deserve this. You let us all die._

 

And so she didn't. Because she deserved this. She let them all die.


	7. Chapter 7

She lay there, ready to bleed out.

 

It'd be slow, since the pick that was driven through her hands had been sure to slow the flow by plugging up the wounds it created, but she would wait.

 

Maybe she'd starve before that happened, or maybe he'd come back and finish her off...

 

But for some reason, she still had HOPE, though she didn't know what for; this world was hopeless as is, and same for all who reside in it, especially her.

 

...So why did she have HOPE, again? Was it HOPE that something would change, or was it something else?

 

She frowned, tightly shutting her eyes. It was getting drafty in here, with her clothes in tatters like they were.

 

Her body had started to fight against herself, practically liquefying as she struggled. She didn't notice it at first when the pick was pulled out from the ground, and she didn't notice until a long while after. Her body was on auto-pilot.

 

The pick fell to the ground with a metallic clatter as she stood up.

 

Her melting body had already formed a weak covering of the wounds, enough to heal in a few days at most.

 

As she stood, her body reformed properly, and, for once in her long life...

 

She felt DETERMINED.


	8. Chapter 8

She crumbled up the small package of food, now left empty, before dropping it on the desk again.

 

She's been much more hungry lately, yet she was unsure as to why considering she always ended up throwing it up a few days later.

 

She thought to herself of theories, eyes sliding shut.

 

Maybe she has an intestinal blockage... but that wouldn't explain her hunger, would it?

 

What about... some sort of disorder had formed? No, she didn't have body image issues, really...

 

She sighed, leaning back in her chair and staring at the ceiling, making out tiny designs in the cracks as if they were the star stones in Waterfall.

 

She hadn't left her lab in - with a quick look at the calendar - a few months. Monsters seemed to age really slowly compared to humans, she supposed.

 

The boredom was truly beginning to get to her, yet she'd rather admit that the outside didn't feel nearly as safe as she had wished it would be. Not as though she has been out there in a while, but she can tell it most likely won't be pleasant.

 

Her stomach churned as she reached for another food packet, and she sighed as her mind wandered yet again.

 

What is making her feel this way...?


	9. Chapter 9

**Summary for the Chapter:**

> Nine is a really lucky number for Undyne.
> 
> I mean, what other story has the chapter she was in?
> 
> She's such a lucky girl.
> 
> (Also, I've been planning this twist for a while but never put it in the tags for the reason of it being a twist. Surprised no one found out or guessed yet.)

She stared in pure shock, eyes wide.

 

She grabbed her glasses, pulling them off of her face, and wiped them against her pants, before putting them back on. The glow was still there.

 

She felt the blood drain from her face, feeling woozy, like she was going to faint.

 

...It explained a lot.

 

The sudden HOPE, as if she felt something new was headed her way, something good.

 

The eating issues.

 

The moodiness.

 

Everything led to one thing, one thing she _never_ dared to imagine.

 

She put a hand over her stomach, the mirror reflecting the small SOUL that glowed through her skin.

 

Monsters reproduce in a variety of ways. 

 

The most common is sexual, yet some monsters who didn't have the needed 'parts' would tear off a piece of their SOUL, mend it with that of their mate's broken off SOUL piece, and they would form a small 'cocoon' for the monster child to grow in.

 

In this case, she only had one person to blame.

 

She felt choked up. She didn't want this. She didn't want him. She didn't want it.

 

 _You deserved it, didn't you?_ their voice echoed, their hand landing on hers. _You said so yourself. You could've stopped him, but you didn't. You must've wanted it._ they blamed. 

 

Against all of her better judgement, she felt like they were right.

 

_She could've stopped him, but she didn't. It's her fault. She must've upset him. She tried to hurt him, and he fought back, didn't he? Maybe she led him on earlier. Maybe the clothes she wore were too risque. It was her fault. It still is her fault._

 

These words repeated like a mantra, and she didn't notice how her sharp nails were digging into her skin. The red freckles really were a contrast to the bright, pastel blue, but the glowing blood that slowly dripped out was like a mural.

 

Like paint. It reminded her of the Echo Flowers she studied once in Waterfall. The glowing blue as they repeated whatever they had heard prior.

 

She felt like an Echo Flower at the moment, with how she kept repeating those words both aloud and in her head, as the glowing blood trailed down to her pants, dripping down her legs, and falling to the ground with a cute little _'plip'_ that knocked her from her trance.

 

She dug her fingers in deeper, mouth shutting abruptly with the mantra suddenly ceasing with it. Almost as if the record was suddenly torn from the player and smashed on the ground, vinyl chips shattered and clank against the floor, like music.

 

She slowly pulled her hand away, holding it to her face.

 

"I deserve it." she mumbled quietly, pressing her bloody handprint over the mirror, trying to 'censor' her face with the glowing blood.

 

All that was left in the mirror was a bright cyan glow, and her shirtless form. Over her chest was her SOUL, glowing and pulsing through her body, the upside-down white heart big enough to be held in both hands, the size of a single one. Over her stomach was the new SOUL, beating at its own tempo. 

 

She felt corrupted.

 

But...

 

_She deserved it._


End file.
